1. Field of the Invention
The present invention relates to an image signal processing device for processing pixel signals that are obtained by a single CCD system, and to a method of processing the pixel signals.
2. Description of the Related Art
Conventionally, several color imaging systems including the single-CCD system, the 3-CCD system, and the frame sequential method are known. In particular, the single-CCD system is used in a household video camera and in an electronic endoscope because it can output three or four color signals while having simple structure.
In the single-CCD system, a color filter array, which is composed of magenta (Mg), green (G), cyan (Cy), and yellow (Ye) color filters arranged in a mosaic array, is provided on a light-receiving surface of the CCD. On the CCD, the pixels having Mg, G, Cy, and Ye filters generate the Mg, G, Cy, and Ye color signals, respectively.
The pixel data of each pixel are read out by some kind of scanning method, for example, a progressive scan. In the progressive scan method, pixel data for each of all the pixels is independently read out, and then interpolation signals for all the pixels are generated by conducting pixel interpolation using the pixel data.
A method for the pixel interpolation of the color signals is shown in Japanese Unexamined Patent Publication (KOKAI) NO. H10-234047. In this method, the Mg, G, Cy, and Ye interpolation signals for the center of a 4×4 matrix (pixel matrix) are generated by determining which position in the 4×4 matrix the same color pixels are located on.
In the CCD used in the above method, two different color pixels alternate, both in the row direction and in the column direction. Due to this pixel arrangement, the same color pixels in all the 4×4 matrices are arranged in the same pattern; therefore, it is easy to determine which position in the 4×4 matrix the same color pixels are located on.
However, there are several types of pixel arrangements on the single CCD; for example, the color difference sequential array as shown in Japanese examined Patent Publication (KOKOKU) NO. H6-28450, and the Bayer array as shown in Japanese Unexamined Patent Publication (KOKAI) NO. S51-112228.
In the color difference sequential array, it is difficult to determine at which position in the pixel matrix the same color pixels are located according to the pattern, because the Ye pixels and the Cy pixels do not alternate in the same column; namely, the array patterns are different between the Ye pixels and the Cy pixels. Similarly, it is difficult to determine which position in the 4×4 matrix the same color pixels are located at according to the pattern, because the array patterns are different between Y (luminance) pixels and first (or second) color C1 or C2 pixels in the Bayer array. Namely, when the pixel signals are read out in a progressive scan in a CCD having one of these pixel arrangements, it is difficult to conduct pixel interpolation using the method as described above.